Some engine control strategies may estimate torque based on air-fuel ratio and other operating parameters in order to control engine output. Furthermore, some engine control strategies advantageously employ different modes of engine operation, such as for example, a fuel injector cut-out mode which may include a cylinder group that pumps air without injected fuel in order to improve fuel economy and engine efficiency.
One approach attempts to estimate engine torque based on various parameters including the air-fuel ratios of the cylinders combusting air and fuel in a fuel injector cut-out mode. See, for example, U.S. Pat. No. 6,758,185.
However, the inventors herein have recognized that this approach may have some disadvantages. For example, in an engine system with an asymmetric exhaust sensor configuration, some modes of operation may cause the asymmetric sensor configuration to produce confounded air-fuel ratio measurements, which in turn, may cause greater errors in engine torque estimation.
The above issue may be addressed by, in one example, a system for a vehicle comprising: an engine including a first cylinder group and a second cylinder group; a linear exhaust gas sensor coupled exclusively to the first cylinder group; a switching exhaust gas sensor coupled exclusively to the second cylinder group; and a controller configured to operate the engine in at least a first mode and a second mode, where in the first mode the first and second cylinder groups combust air and fuel, where in the second mode at least one of the first and second cylinder groups combusts air and injected fuel and the other one of the first and second cylinder groups pumps air without injecting fuel, and where the controller is further configured to estimate torque of the engine in each of the first and second modes of operation based on the air-fuel ratio of the first cylinder group and the air-fuel ratio of the second cylinder group independent of the switching sensor and dependent on the linear sensor.
In this way engine torque may be estimated in a robust manner allowing for an engine control strategy to include different modes of operation in an engine system with an asymmetric exhaust gas sensor configuration. In particular, engine torque may be estimated even when the exhaust gas sensors produce confounded air-fuel readings due to the cylinder groups operating at different air-fuel ratios.